If you are just planning on using it for webbrowsing, desktop, and other 2d acceleration tasks or minimal 3d acceleration, it may increase it by a few degrees but likely won't make much of a difference.
However, if you currently play games at 1440x900 and make the jump in resolution to 1920x1200 it will likely get hotter working harder to push those extra 3d pixels in a high resolution 3d game
Simply stated - Desktop usage will be little or no temp increase, games will likely increase temp if at full resolution.